Generally, amphiphilic co-networks comprise hydrophilic and hydrophobic polymers that can swell in both polar and non-polar solvents. Additionally, amphiphilic networks and/or co-networks can be used to produce polymer films that swell in both polar and non-polar solvents. Accordingly, films made from amphiphilic polymer networks and/or co-networks have been found to be desirable in the production of various articles including, but not limited to, contact lenses.
In one instance, amphiphilic co-networks (APCNs) are two-component networks of covalently interconnected hydrophilic/hydrophobic phases of co-continuous morphology; as such they swell both in water and hydrocarbons and respond to changes in the medium by morphological isomerization (“smart networks”). APCNs were conceived and first produced in Akron in 1988 and since that time have been intensely investigated by academic and industrial researchers around the world
FIG. 1 helps to visualize the morphology of an APCN and its response to changing the solvent milieu.
First generation APCNs were prepared by the free radical copolymerization of select hydrophilic monomers (e.g., dimethyl acrylamide (DMAAm)) with methacrylate-capped polyisobutylene (MA-PIB-MA) as the crosslinker; thus these early APCNs comprised various hydrophilic main chains crosslinked by the hydrophobic PIB chains. Hydrophilic/hydrophobic domain co-continuity (percolation) was demonstrated by swelling experiments using water and hexane. The APCNs were found to be biocompatible in rats. Devices using such APCNs that contain porcine pancreatic islets enveloped/immunoisolated therein, when implanted into diabetic rats, were found to reduce their hyperglycemia.
Second generation APCNs were prepared by combining a suitable polyethylene glycol) (PEG) with suitable polydimethylsiloxane (PDMS) sequences. The motivation to develop second generation APCNs was to create membranes that allow the simultaneous rapid countercurrent transport of water (or aqueous solutions) and oxygen, a highly hydrophobic entity. Water diffuses via the hydrophilic channels provided by the hydrophilic PEG domains while O2 permeates via the oxyphilic PDMS domains. The synthesis was simplified and then membranes with controlled amounts and molecular weights of hydrophilic/hydrophobic sequences were prepared. As expected, these APCNs were biocompatible; however, later we found that the PEG segments oxidatively degraded under simulated extended (e.g., weeks, months) implant conditions.
To overcome this degradation issue relating to PEG-containing APCNs for biological applications, third generation APCNs were developed in which the PEG segments were replaced by the oxidatively/hydrolytically/biologically resistant hydrophilic segment PDMAAm. The synthesis required the preparation of a novel crosslinking agent and a fundamentally new synthetic strategy. These APCNs were found to be eminently suitable for immunoisolation of pancreatic tissue, and became the subject of several patent applications.
On the other hand, the amphiphilic co-networks of the present invention are designed to create more versatile physically crosslinked processable recyclable APCNs. In one instance, there is a need in the art for reliable synthesis routes for thermoplastic amphiphilic co-networks (TP-APCNs) that can be processed thermally (by molding, injecting, extruding, etc.) or by solution techniques (casting, dipping, drawing, etc.).